1. Field of the Invention
The present invention relates to base particles for supporting a surfactant useful for improvements in performance, mainly as laundry detergents (hereinafter referred to as “base particles”), with improved detergency, detergent particles, and a process for preparing the above-mentioned base particles. In addition, the present invention relates to a zeolite for a laundry detergent.
2. Discussion of the Related Art
In the development of high-density powdery detergents in the latter half of 1980's, the compactness of the powdery detergents greatly contributed to transport or carrying and housing ability of the detergents. Therefore, at present, compact detergents (high-density detergents) have become the main stream.
As to a process for preparing a high-density detergent, numerous studies have been so far made. One of its example is a technique for obtaining detergent particles comprising supporting a surfactant to base particles obtained by spray-drying as disclosed in, for instance, WO 99/29830. The detergent particles have the features of fast dissolubility and high disintegration.
Because the fast dissolubility and the high disintegration of the detergent particles as mentioned above advantageously act on the detergency, the present inventors have further studied in detail regarding the relationship of the dissolubility and the disintegration with the detergency of the detergent particles. As a result, they have found for the first time that the zeolite added as a water-insoluble inorganic compound greatly affects the detergency of the detergent particle. Specifically, each of 6 kinds of zeolite A-type having the same level of cationic exchange ability is added to base particles, to give detergent particles. The detergency of each group of the detergent particles is determined. As a result, the base particles obtained by adding each of the zeolites exhibit different cationic exchange abilities, and it has been clarified that such a difference of the cationic exchange abilities of each group of the base particles greatly affect the detergency of the detergent particles prepared from the base particles. The present inventors have pursued further studies on factors and causations for changing the cationic exchange ability of the base particles described above. As a result, they have found for the first time that the aggregation form of the added zeolite is greatly affected such that the more even the distribution of the aggregate particle diameter of a secondary aggregate obtained by aggregating primary particles of the zeolite alone, the higher the cationic exchange ability of the base particles containing the zeolite. Therefore, a zeolite having a more even distribution of the aggregate particle diameter than the above zeolite is prepared. The zeolite is added to base particles, and as a result, it has been confirmed that the resulting base particles exhibit an unexpectedly high cationic exchange ability.
The aggregation state of the zeolite can be acknowledged by using an electron microscope. Generally, it has been confirmed that cubic or spherical primary particles are collectively gathered to form a secondary aggregate. The particle diameter of the secondary aggregate is determined to obtain a distribution of the aggregate particle diameter. By subjecting the distribution of the aggregate particle diameter to a statistic treatment, the degree of dispersion of the distribution of the aggregate particle diameter is found. In other words, as a measure for expressing the degree of dispersion of the distribution of the aggregate particle diameter, it is convenient to use a standard deviation. However, the standard deviation can be applied to comparisons of those zeolites having the same average aggregate particle diameter. Therefore, in a case of those zeolites having different average aggregate particle diameters, a value obtained by dividing the standard deviation of the distribution of the aggregate particle diameter by the average aggregate particle diameter (in some cases multiplied by 100 and expressed as %, which is referred to as a variation coefficient in statistics) is a measure for expressing dispersion.
The variation coefficients of the distribution of the aggregate particle diameter of the above 6 zeolites are from 30.5% to 64.9%. It has been confirmed that the smaller the variation coefficients of the zeolite, namely those having an even distribution of the aggregate particle diameter of the zeolite, the higher the cationic exchange abilities of each group of the base particles containing the zeolite, and the higher the detergency of the resulting detergent particles.
In the zeolite for detergent builders, it has been known in the art that those zeolites having a narrow distribution of the aggregate particle diameter are preferable. For instance, the zeolite obtained by the process disclosed in Japanese Patent Laid-Open No. Sho 53-102898 has a narrow distribution of the aggregate particle diameter. The reasons for narrowing the distribution of the aggregate particle diameter are such that exceedingly fine particles tend to be adhered to fabrics and that coarse grains tend to be settled at bottom. Therefore, an object of this publication is to narrow the distribution of the aggregate particle diameter of the resulting zeolite used for laundry detergents from the viewpoint of prevention of residuality of zeolite on clothes. In addition, a zeolite obtained by the process disclosed in Japanese Patent Laid-Open No. Sho 54-147200 also has an aggregate particle diameter of roughly from 1 to 5 μm, from the viewpoint of re-deposition on clothes and the like. As described above, although the conventionally known zeolite has a narrow distribution of the aggregate particle diameter, the zeolite has a variation coefficient of from 29.9 to 43.0%. Therefore, a zeolite having a very even particle diameter distribution as 29% or less is not disclosed in the publication. Also, in WO 99/29830, a zeolite manufactured by Tosoh Corporation, which has an average aggregate particle diameter of 3.5 μm and a variation coefficient of 30.5%, is added to base particles. Therefore, the zeolite does not have any effects for improving the cationic exchange ability of the base particles as taught in the present invention; in fact, its detergency has been insufficient.
Accordingly, an object of the present invention is to provide base particles having excellent cationic exchange ability, and a process for preparing the base particles.
Another object of the present invention is to provide a zeolite for a laundry detergent used for the process for preparing the base particles, and detergent particles having excellent detergency.
These and other objects of the present invention will be apparent from the following description.